CN102128881B - Method for monitoring Lamb wave engineering structural damage by utilizing signal decomposition - Google Patents

Abstract

The invention discloses a method for monitoring Lamb wave engineering structural damage by utilizing signal decomposition, which comprises the following steps: collecting the Lamb wave healthy reference signals fhji of an engineering structure in a healthy state, wherein i and j can be 1, 2, 3,...; when the structure is damaged, collecting all the Lamb wave response signals f'ji of the damaged structure under the condition of an inspiring/sensing channel; utilizing the correlation operation to extract all the Lamb wave damage scattered signals of the damaged structure under the condition of the inspiring/sensing channel; obtaining the damage position and scope according to the characteristic parameters acquired in the steps above, thereby analyzing and judging the health condition of the monitored structure. According to the method, based on the condition of the traditional structural damage monitoring device, the Lamb wave damage scattered signals in a damage monitoring system are extracted by using the related treatment, thereby increasing the accuracy and stability of the monitoring system.

Description

Lamb wave engineering structure damage monitoring method based on signal decomposition

technical field

The present invention relates to a method for active Lamb wave damage monitoring of plate engineering structures, in particular to a method for extracting damage scattering signals of Lamb wave structures in active health monitoring so as to correctly realize damage monitoring of engineering structures.

Background technique

With the continuous improvement of structural safety and reliability requirements, the on-line monitoring and diagnosis of structural damage has attracted more and more attention. In order to prevent disasters or losses caused by structural damage, effective monitoring of plate structures is necessary.

The on-line monitoring of structural damage requires that the relevant signal generation and acquisition equipment should be relatively simple, and the monitoring must have high accuracy and real-time performance. The damage monitoring of plate structures generally adopts the method of active Lamb wave, that is, a certain number of actuators and sensors (such as piezoelectric elements) are integrated on the surface or inside of the structure. In addition, the entire monitoring system also includes signal generating devices, power Amplifiers, signal amplifiers, and data acquisition equipment, etc., first excite a certain waveform into the structure during monitoring, and collect the response of the structure and the scattered waves generated by the damage through the sensor, and collect them in the computer. By comparing the difference between the response signals before and after the structure damage, Scattering signals of structural damage are obtained, and then the location and range of damage are determined by computer programs based on information such as the arrival time and phase of damage scattering waves. According to the Lamb wave propagation theory, there are dispersion and mode transformations in the propagation process of Lamb waves in plate structures, and the propagation speeds of Lamb wave signals with different frequencies are also different. The energy of the Lamb wave scattering signal caused by structural damage is generally very small, and the energy of the Lamb wave propagation signal excited by the exciter in the structure is often more than one order of magnitude different. Since the propagation of Lamb waves in the plate structure is non-directional, the method of directly subtracting the response signals before and after structural damage is mostly used to obtain the Lamb wave damage scattering signal. At this time, the piezoelectric element, signal power amplifier and data acquisition equipment Affected by changes in the environment and its own parameters will directly interfere with the correct extraction of damage scattering signals, and deviations will easily occur. This problem brings difficulties to the correct analysis of the acoustic wave propagation process and the extraction of characteristic parameters of the damage scattering signal, especially in the damage monitoring of composite plate structures, because the Lamb wave signal propagation is complex and the structure absorbs the signal quickly, so that The problem gets more complicated. For example: At present, the aircraft structure uses a large number of composite materials, and the structure is very complex. To study the online damage monitoring of the aircraft structure, the damage scattering signal must be correctly extracted first. Therefore, it is necessary to analyze the signal propagation law of the Lamb wave and correctly extract the Lamb wave damage scattering signal to ensure the extraction of the characteristic parameters related to the damage and ensure the authenticity, validity and stability of the monitoring results.

Based on the above considerations, the present inventors researched and improved the existing method for extracting scattering signals of structural damage, and this case arose from this.

Contents of the invention

The technical problem to be solved by the present invention is to provide a Lamb wave engineering structure damage monitoring method using signal decomposition for the defects and deficiencies in the above-mentioned background technology. On the basis, the correlation processing is used to realize the extraction of Lamb wave damage scattering signal in the damage monitoring system, which improves the accuracy and stability of the monitoring system.

The present invention is for solving the problems of the technologies described above, and the technical solution adopted is:

A method for monitoring damage of a Lamb wave engineering structure utilizing signal decomposition, comprising the steps of:

(1) Arrange a group of piezoelectric elements on the engineering structure to be monitored to form a sensing/excitation array, where the piezoelectric element as the excitation element is set as P _j , and the piezoelectric element as the sensing element is set as P _i , where i, j = 1, 2, 3, ...;

(2) Acquisition of Lamb wave health reference signals fh _ji under all excitation/sensing channels of the engineering structure in the structural health state, where i, j = 1, 2, 3, ...;

(3) When the structure is damaged, collect the Lamb wave response signals f' _ji after the structural damage under all excitation/sensing channels, where i, j = 1, 2, 3, ...;

(4) Extract the Lamb wave damage scattering signals after structural damage under all excitation/sensing channels, the specific content is:

(41) Cross-correlate the Lamb wave health reference signal fh _ji obtained in step (2) with the structurally damaged Lamb wave response signal f' _ji obtained in step (3), and obtain the peak time t _ji and The peak value U _ji , and divide the peak value U _ji by the autocorrelation peak value of fh _ji to obtain the amplitude value u _ji of the Lamb wave healthy reference signal;

(42) Multiply the Lamb wave health reference signal fh _ji with its corresponding amplitude u _ji to obtain the health signal part fh' _ji in the Lamb wave response signal after structural damage;

(43) Taking the time series of the Lamb wave response signal f' _ji after the structural damage as a reference, and taking the time t _ji under the reference time series as the starting time of the signal fh' _ji , according to the corresponding time point, the Lamb wave after the structural damage The wave response signal f' _ji is correspondingly subtracted from the signal fh' _ji to obtain the Lamb wave structural damage scattering signal fd _ji .

(5) According to the characteristic parameters obtained in the previous steps, the location and scope of the damage are obtained, so as to analyze and judge the health of the monitored structure.

The detailed steps of the above step (2) are:

(21) Under the healthy state of the structure, the Lamb wave ultrasonic signal is loaded on P _j as the excitation element through the function generator and the power amplifier, and the excitation signal is excited in the structure;

(22) Sequentially select each piezoelectric element P _i as the sensing element, where i = 1, 2, 3, ..., through the charge amplifier, the Lamb wave structure response signal under the excitation of P _j is sensed, amplified and collected into the control computer , get the Lamb wave response signals f _ji of all excitation/sensing channels under the healthy state of the structure, where i, j = 1, 2, 3, ...;

(23) For each of the aforementioned Lamb wave response signals f _ji , where i, j = 1, 2, 3, ..., perform normalization processing according to their peak values, and obtain the Lamb wave health reference signal fh _ji , where i, j = 1, 2, 3, . . .

In the above step (21), the excitation signal is a narrowband signal.

The detailed steps of the above step (3) are:

(31) When the structure is damaged, the Lamb wave ultrasonic signal is loaded on the P _j as the excitation element through the function generator and the power amplifier, and the narrow-band excitation signal is excited in the structure;

(32) Sequentially select each piezoelectric element P _i as the sensing element, where i = 1, 2, 3, ..., through the charge amplifier, the Lamb wave structure response signal under the excitation of P _j is sensed, amplified and collected into the control computer In , the Lamb wave response signals f' _ji of all excitation/sensing channels when the structure is damaged are obtained, where i, j =1, 2, 3, . . .

After adopting the above scheme, the basic principle borrowed by the present invention is: after the frequency-thickness product is determined, the propagation characteristics of the Lamb wave propagation signal are basically determined, and parameters such as its velocity are also determined. The damage in the structure is a scatterer relative to the Lamb wave propagation, which will scatter the Lamb wave propagation signal. The difference before and after structural damage is that there are more damage scatterers. Therefore, for the Lamb wave structural response signal, the response signal after structural damage includes both the response signal in the healthy state of the structure and the scattering caused by damage. Signal. The sources of these two signals are different from the moment of occurrence, and the energy of the former is much greater than that of the latter. When the environment or equipment parameters change, such as temperature changes, the amplitude of the response signal will inevitably change, but it will not change the propagation law of the Lamb wave signal, that is, the relative time and peak of each wave packet in the response signal will not change. , only the amplitude of the entire signal changes. At this time, the Lamb wave response signal in the structural health state is used as the reference signal, and the correlation calculation is carried out with the structural response signal after damage. The health response signal part of the structural response signal is actually an autocorrelation operation. It is completely correlated and its correlation value is the largest. Therefore, the time when the maximum correlation value appears must be the time when the health response signal part appears. The ratio of the correlation maxima is the amplitude of the healthy response signal. Then the health response signal part of the structural response signal after damage is obtained, and the Lamb wave scattering signal caused by damage is obtained after subtracting this part of the signal according to the corresponding time. The invention can effectively eliminate the interference caused by environment and equipment parameter changes on the extraction of Lamb wave damage scattering signals, and is beneficial to promoting the popularization and application of structural health monitoring technology.

Description of drawings

Fig. 1 is the layout schematic diagram of sensing/excitation array in the present invention;

Fig. 2 is the waveform time-domain figure of narrowband excitation signal among the present invention;

Fig. 3 a is a Lamb wave response signal waveform diagram under a certain channel in the present invention under the excitation of the narrowband signal shown in Fig. 2 under the healthy state of the structure;

Figure 3b is a waveform diagram after normalizing the signal shown in Figure 3a;

Fig. 4 is a Lamb wave response signal waveform diagram when the structure is damaged under the excitation of the narrowband signal shown in Fig. 2 under a certain channel in the present invention;

Figure 5 is the comparison between the excitation signal, the Lamb wave structural response signal after the structural damage shown in Figure 3a, and the difference signal obtained by direct corresponding subtraction between the Lamb wave response signals before and after the structural damage shown in Figure 3a and Figure 4 schematic diagram;

Fig. 6a is a waveform schematic diagram of performing cross-correlation operation on the signals shown in Fig. 4 and Fig. 3b in the present invention;

Figure 6b is the amplitude and occurrence time of the structural health state response signal obtained from the correlation calculation structure shown in Figure 6a;

Figure 6c is the comparison between the response signal in the structural health state contained in the structural response signal after damage and the original signal after being separated;

Fig. 7 is a schematic diagram of a Lamb wave damage scattering signal obtained by using the present invention.

Detailed ways

The realization process of the present invention will be described in detail below in conjunction with accompanying drawing.

The invention provides a Lamb wave engineering structure damage monitoring method utilizing signal decomposition, comprising the following steps:

(1) Arrange a group of piezoelectric elements on the engineering structure to be monitored to form a sensing/excitation array, where the piezoelectric element as the excitation element is set as P _j , and the piezoelectric element as the sensing element is set as P _i , And i, j = 1, 2, 3, ...;

In this embodiment, as shown in Figure 1, i =1, 2, j =1, these 3 piezoelectric elements are all fixed on the test piece, and the test piece is an epoxy glass fiber reinforced composite material plate , with a size of 800mm×200mm×2mm; the three piezoelectric elements are arranged in a straight line, with the center point of the specimen as the coordinate origin, and the coordinates of the three piezoelectric elements A, B, and C are (50mm, 0mm), (0mm , 0mm), (-50mm, 0mm), in this embodiment, the piezoelectric element A is used as the excitation element, and the other two piezoelectric elements B and C are used as the sensing element, and the damage type is typical through-hole damage, and the implementation In the example, an electric drill is used to drill a hole with a diameter of about 4mm at the coordinates (0mm, 35mm) to form a through-hole damage, and the response signals before and after the damage are collected and analyzed respectively;

(2) Acquisition of Lamb wave health reference signal ( fh _ji ) under structural health status, the details of which are:

(21) Under the healthy state of the structure, the Lamb wave ultrasonic signal is loaded on the P _j (that is, the piezoelectric element A) as the excitation element through the function generator and the power amplifier, and the narrow-band excitation signal is excited in the structure. In this implementation In the example, the narrowband excitation signal is a sinusoidal modulation signal with a center frequency of 30KHZ, as shown in Figure 2;

(22) Each piezoelectric element P _i ( i = 1, 2) is selected in turn as the sensing element, and the Lamb wave structure response signal excited by P _j is sensed, amplified and collected into the control computer through the charge amplifier, and all Lamb wave response signals ( f _ji ) ( i, j = 1, 2, 3, ...) under the excitation/sensing channel in the healthy state of the structure, as shown in Figure 3a, when j = 1, i = 2 The obtained Lamb wave response signal in the healthy state of the structure ( f ₁₂ );

(23) For each of the aforementioned Lamb wave response signals ( f _ji ) ( i, j = 1, 2, 3, ...), normalize them respectively according to their peak values to obtain the signal ( fh _ji ) ( i, j =1, 2, 3,...), which is the healthy reference signal of the Lamb wave, and the healthy reference signal of the Lamb wave when j =1, i =2 can be shown in Figure 3b;

(3) When the structure is damaged, repeat steps (21) to (22) to obtain the Lamb wave response signals ( f' _ji ) after structural damage under all excitation/sensing channels ( i, j = 1, 2, 3 ,…), its details are:

(31) When the structure is damaged, the Lamb wave ultrasonic signal is loaded on the P _j as the excitation element through the function generator and the power amplifier, and the narrow-band excitation signal is excited in the structure;

(32) Sequentially select each piezoelectric element P _i ( i = 1, 2, 3, ...) as the sensing element, and sense, amplify, and collect the response signal of the Lamb wave structure under the excitation of P _j through the charge amplifier into the control computer , get the Lamb wave response signal ( f' _ji ) ( i, j =1, 2, 3,…) of all excitation/sensing channels when the structure is damaged, and the signal when j =1, i =2 ( f '12 ) as shown in Figure ₄ ;

Comparing Figure 4 with Figure 3a, it can be seen that due to the long time interval between the collected signal and the healthy state of the structure, the environmental parameters have changed (such as temperature), thus affecting the parameters of the sensing element and amplifier, and the amplitude of the signal Specifically, the system noise signals collected in the early stage are equivalent and have not changed significantly, which indicates that the parameters of the acquisition system have not changed, and the amplitude of the response signal has decreased to a certain extent. According to the damage and excitation / sensor array position relationship, the damage scattering signal will not affect the peak amplitude of the main wave, so the response signals before and after the structural damage obtained in this case cannot be directly subtracted.

On the other hand, as shown in Fig. 5, the excitation signal, the Lamb wave structural response signal after the structural damage shown in Fig. 3a, and the Lamb wave response signal ( f ₁₂ ) before and after the structural damage shown in Fig. 3a and Fig. 4 are compared with ( f' ₁₂ ) Comparing the difference signal obtained by subtraction, it can be seen from the figure that the waveform of the difference signal is basically the same as the structural response signal after damage, so the difference signal at this time is actually mainly due to the piezoelectric sheet And the deviation caused by the change of the amplification system parameters cannot correctly reflect the signal change caused by the damage.

(4) Extract the Lamb wave damage scattering signals after structural damage under all excitation/sensing channels, still taking the signal collected when P ₁ is the excitation and P ₂ is the sensing as an example, the specific content is as follows:

(41) Cross-correlate the Lamb wave health reference signal ( fh ₁₂ ) obtained in step (2) with the structurally damaged Lamb wave response signal ( f' ₁₂ ) obtained in step (3), and obtain the peak value of the calculation result Time t ₁₂ and peak value U ₁₂ are shown in Figure 6a, and the peak value U ₁₂ is divided by the autocorrelation peak value ( fh ₁₂ ) to obtain the amplitude value u ₁₂ of the Lamb wave health reference signal, which can be referred to in Figure 6b Show;

Repeat the above process to get t _ji and u _ji for all values of j and i ;

(42) Multiply the Lamb wave healthy reference signal ( fh ₁₂ ) with its corresponding amplitude u ₁₂ to obtain the healthy signal part ( fh' ₁₂ ) of the Lamb wave response signal after structural damage, as shown in Figure 6c, the ( fh' ₁₂ ) is compared with the original signal ( f' ₁₂ ), it can be seen that the main peaks of the structural response signal before and after damage are basically the same, eliminating the influence of environmental parameter changes;

(43) Taking the time series of the Lamb wave response signal ( f' ₁₂ ) after structural damage as the benchmark, and taking the time t _ji under the benchmark time series as the starting time of the signal ( fh' ₁₂ ), according to the corresponding time point, the The Lamb wave response signal ( f' ₁₂ ) and the signal ( fh' ₁₂ ) are subtracted correspondingly after the structural damage, and the Lamb wave structural damage scattering signal ( fd ₁₂ ) is obtained, as shown in Fig. 7, at this time, the wave packet of the damage scattering signal is revealed ;

Repeat the above process to obtain damage scattering signals ( fd _ji ) for all values of j and i .

(5) According to the characteristic parameters such as the arrival time and phase of each damaged scattering signal wave packet obtained in the previous steps, the position and range of the damage can be obtained (ellipse positioning method, time reversal imaging method, etc. can be used), so as to analyze and judge The health of the monitored structure.

It should be noted that the number of piezoelectric elements used as the excitation/sensing array can be determined according to the actual situation of the structure to be monitored. In theory, three piezoelectric elements can form a monitoring unit. A sensing network can be formed by arranging a plurality of piezoelectric elements and carried out by means of scanning, and the specific steps of monitoring each unit in the network are the same.

In summary, the method provided by the present invention has the following advantages:

(1) The accuracy of the structural damage monitoring method based on active Lamb wave technology is improved, which is conducive to the practical application of this technology;

(2) The method of the present invention eliminates the influence of environmental parameters on the monitoring system and the excitation/sensing array, and the system can be measured without preheating during the monitoring process, which improves real-time performance;

(3) The method of the present invention can be implemented by using existing hardware systems without changing or adding equipment and parameters during the implementation process;

(4) The implementation method of the present invention is simple, without prior knowledge of the monitoring object and the sensor array, and only processes the response signals before and after structural damage.

The above embodiments are only to illustrate the technical ideas of the present invention, and can not limit the protection scope of the present invention with this. All technical ideas proposed in accordance with the present invention, any changes made on the basis of technical solutions, all fall within the protection scope of the present invention. Inside.

Claims (4)

1. a Lamb wave engineering structural damage monitoring method utilizing signal decomposition, is characterized in that comprising the steps: (1) Arrange a group of piezoelectric elements on the engineering structure to be monitored to form a sensing/excitation array, where the piezoelectric element as the excitation element is set as P _j , and the piezoelectric element as the sensing element is set as P _i , where i,j=1,2,3,...; (2) Acquisition of Lamb wave health reference signals fh _ji under all excitation/sensing channels of the engineering structure in the structural health state, where i, j=1, 2, 3, ...; (3) When the structure is damaged, collect the Lamb wave response signals f' _ji of the damaged structure under all excitation/sensing channels, where i, j=1, 2, 3, ...; (4) Extract the Lamb wave damage scattering signals after structural damage under all excitation/sensing channels, the specific content is: (41) Cross-correlate the Lamb wave health reference signal fh _ji obtained in step (2) with the structurally damaged Lamb wave response signal f' _ji obtained in step (3), and obtain the peak time t _ji and The peak value U _ji , and divide the peak value U _ji by the autocorrelation peak value of fh _ji to obtain the amplitude value u _ji of the Lamb wave healthy reference signal; (42) Multiply the Lamb wave health reference signal fh _ji with its corresponding amplitude u _ji to obtain the health signal part fh' _ji in the Lamb wave response signal after structural damage; (43) Taking the time series of the Lamb wave response signal f' _ji after the structural damage as a reference, and taking the time t _ji under the reference time series as the starting time of the signal fh' _ji , according to the corresponding time point, the Lamb wave after the structural damage The wave response signal f' _ji is correspondingly subtracted from the signal fh' _ji to obtain the Lamb wave structural damage scattering signal fd _ji ; (5) According to the characteristic parameters of the Lamb wave structural damage scattering signal fd _ji obtained in the previous steps, the location and range of the damage are obtained, so as to analyze and judge the health of the monitored structure. 2. the Lamb wave engineering structure damage monitoring method utilizing signal decomposition as claimed in claim 1, is characterized in that: the detailed steps of described step (2) are: (21) Under the healthy state of the structure, the Lamb wave ultrasonic signal is loaded on P _j as the excitation element through the function generator and the power amplifier, and the excitation signal is excited in the structure; (22) Sequentially select each piezoelectric element P _i as the sensor element, where i=1, 2, 3, ..., through the charge amplifier, the Lamb wave structure response signal under the excitation of P _j is sensed, amplified and collected into the control computer , get the Lamb wave response signal f _ji of all excitation/sensing channels in the healthy state of the structure, where i, j=1, 2, 3,...; (23) For each of the aforementioned Lamb wave response signals f _ji , where i, j=1, 2, 3, ..., perform normalization processing according to their peak values to obtain the Lamb wave health reference signal fh _ji , where i, j = 1, 2, 3, . . . 3. The Lamb wave engineering structure damage monitoring method utilizing signal decomposition as claimed in claim 2, characterized in that: in the step (21), the excitation signal is a narrowband signal. 4. the Lamb wave engineering structure damage monitoring method utilizing signal decomposition as claimed in claim 1, is characterized in that: the detailed steps of described step (3) are: (31) When the structure is damaged, the Lamb wave ultrasonic signal is loaded on the P _j as the excitation element through the function generator and the power amplifier, and the narrow-band excitation signal is excited in the structure; (32) Sequentially select each piezoelectric element P _i as the sensing element, where i=1, 2, 3, ..., through the charge amplifier, the Lamb wave structure response signal under the excitation of P _j is sensed, amplified and collected into the control computer In , the Lamb wave response signals f' _ji of all excitation/sensing channels when the structure is damaged are obtained, where i, j=1, 2, 3, . . .

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